The object of the invention is to provide an anaesthesia-breathing apparatus by means of which gas can be supplied to a patient for artificial respiration, supported respiration, anaesthesia purposes or combinations of such purposes. Such apparatuses which for example are known from Swedish published specification 7308537-5 or U.S. Pat. Nos. 3,814,091 and 3,901,230 comprises a gas chamber connected, on the one hand, to a patient connecting piece and, on the other hand, a respiratory gas receptacle, for example in the form of a respiration bag, a check valve adapted to permit discharge of excess gas from the breathing apparatus to the atmosphere and, optionally, a filter for absorption of carbon dioxide from recirculating breathing gas.
Most closely related with the object of the invention as far as the function is concerned is the anaesthesia-breathing apparatus according to the above-mentioned U.S. Pat. Nos. 3,814,091 and 3,901,230. The apparatus shown fundamentally in FIG. 3 of U.S. Pat. No. 3,901,230 operates substantially in the same way as the apparatus according to the present invention in those cases in which the patient is breathing spontaneously. Both apparatuses operate in this case according to the well-known Magill-narcosis-breathing system. However, use of the known apparatus is used for performing controlled ventilation, or supported ventilation which is a transition form between spontaneous respiration and controlled ventilation, the known has drawbacks which may be dangerous for the patient. In all the embodiments described in U.S. Pat. No. 3,901,230 a closure of the gas discharge valve can take place when the breathing bag is manually operated. If this happens the system is filled with fresh gas causing the pressure to increase. For this reason the provision of a security valve in this system is required in order to prevent the build-up of dangerously high pressures in the lungs of the patient in consequence of the gas supply. In addition the known apparatus requires the provision of a venting valve which upon manual operation permits discharge of gas from the excessively filled system to permit the state of locking to be removed.